1. Field of the Invention
This invention relates to an improved delay arming and safety mechanism for a fuze for a spinning projectile.
2. Prior Art
The fuze of this invention is an improvement on the conventional ball rotor safing and arming mechanical fuze used for medium caliber ammunition, an example of which is the M505A3 point detonating fuze employed in M56 20 mm High Explosive Incendiary ammunition, shown in FIG. 1.
The M505 fuze ball rotor employes a single safety device which is a "C" spring clip and which retains the explosive train, i.e. the detonator and the booster, in an out-of-line position prior to gun launch. This spring clip is defeated when the projectile exits the gun muzzle at the very high spin rate imparted to the projectile by the rifling within the gun barrel. Once the spring clip releases its grip on the out-of-line ball rotor, the rotor, due to spin dynamics, aligns itself so that the detonator within the rotor becomes oriented to the same axis as the firing pin and the booster. At this disposition, the fuze detonator is "armed" and capable of being "initiated" by the firing pin.
A shortcoming of such a ball rotor fuze is that only a single gun launch induced environment, i.e., projectile spin, suffices to arm the fuze. Desirably, a second gun launch induced environment, i.e., setback, should also be required to arm the fuze, and these should be two independent devices to respond respectively to each environment. Thus, if there are two safety devices, then if one device has been omitted in the assembly procedure, the other device may be there to keep the fuze safe.
Typically, these fuzes have a third semi-safing feature comprising a flange on the firing pin, which flange must be sheared off upon impact to free the pin to stab the detonator. Such a shearing process absorbs much kinetic energy and reduces the sensitivity of the fuze to low angle grazing impacts.
There have been many improvements proposed, including Ziemba, U.S. Pat. No. 3,595,169 and Rossman et al, U.S. Pat. No. 4,440,085, which each show a single spring clip which must respond to both setback and spin to release the ball rotor. If this single spring clip has been omitted in assembly, however, the rotor is free and may allow arming of the fuze. Other variations of interest are shown in Thompson, U.S. Pat. No. 2,715,873; Ziemba et al, U.S. Pat. No. 3,397,640; Bayard et al, U.S. Pat. No. 3,871,297; Ziemba, U.S. Pat. No. 4,242,963; Warren et al, U.S. Pat. No. 4,242,964; Weber et al, U.S. Pat. No. 4,458,594; Ziemba, U.S. Pat. No. 4,494,459; and Nicolas et al, U.S. Pat. No. 4,510,869.
Accordingly, it is an object of this invention to precondition arming of a fuze on contemporaneously but independently sensing the presence of adequate spin and setback forces.
A further object is to provide such a fuze with improved sensitivity to a grazing impact.